1. Field of the Invention
The present invention relates to an ignition coil apparatus for an internal combustion engine that is arranged in a plug hole of the internal combustion engine.
2. Description of the Related Art
In the past, as an ignition coil apparatus for an internal combustion engine of so-called full transistor type (hereinafter simply referred to as an ignition coil apparatus) that is arranged in a plug hole, there has been known one which is capable of reducing the consumption of electric power in a primary winding by decreasing the resistance value of the primary winding thereby to supply a large amount of primary current to a primary coil so as to make quicker or faster the rising of the primary current (see, for example, a first patent document: Japanese patent application laid-open No. H11-22604).
In the ignition coil apparatus as constructed above, ignition performance can be improved by reducing the resistance value of the primary coil and increasing the value of an interruption current in a high rotation number region of the engine, but the cross-sectional area of a center core of the ignition coil can not be increased to a satisfactory extent since the center core is arranged in the elongated plug hole. As a result, magnetic saturation occurs in the center core, so the effective inductance of the primary coil is reduced, thus giving rise to a problem that ignition performance can not be improved in a low rotation number region of the engine.